Each year many thousands of children and adults are injured in playgrounds, and public and private reaction and sports facilities as a result of falls on inadequately prepared surfaces. Lawsuits of several million dollars are common where playground accidents have occurred. Insurance companies are now becoming much more selective in granting coverage and in many instances are denying institutions liability protection. Studies reported by the Consumers Product Safety Commission, for instance, have estimated that a head injury tolerance limit for head-first falls of children are 150-200 g's average acceleration for 3 milliseconds or 200-250 g's peak acceleration. Surfaces composed of synthetic materials currently exist that will adequately protect against these levels, but such materials are costly and only a few institutions and businesses can afford the installation expense. For the several hundred thousand public playgrounds in school districts and recreation departments throughout the country, such materials and installations are too costly. Public authorities must rely on less expensive installations, such as sand beds, pea gravel, shredded tires, and mulch. However, no uniform guidelines exist as to amounts and thicknesses of these materials that are required to produce safe g levels in the event of a fall. Furthermore, no apparatus or method is currently available which can be handcarried to a site, used on a frequent basis by individuals unskilled in conducting tests or obtaining test measurements.
The invention herein describes an apparatus and method which will provide these functions. It is simple to operate, measures impact g levels in real time, can be used for hundreds of impact tests without loss of accuracy, is hand portable, and inexpensive. It can be seen from following U.S. patent briefs, that prior art cannot provide the functions provided by the current apparatus and method.
In Kirkland U.S. Pat. No. 4,492,111, the invention relates to a projectable penetrometer which provides mechanisms for measuring rheological and other properties as well as electrical resistance and resistivity of materials, and/or acoustic monitoring of various types of remote or otherwise inaccessible surfaces including land areas, sea and river bottoms. The apparatus employs a multitude of sensing elements and is further characterized by the presence of at least three electrode pairs. As onboard power supply is included together with telemetry equipment to generate ground characteristics and transmit such signals. In use, the device is dropped or thrust from the host vehicle such as a ship, aircraft or spacecraft and allowed to penetrate the inaccessible surface. It is then dragged along a pre-described track as meansurements are telemetered to the host vehicle. Re-tracking provides comparative information from that received by the initial track.
This apparatus is expensive to manufacture and operate, cannot be easily transported to a test site and requires highly skilled individuals to operate and interpret the data.
Baker's invention U.S. Pat. No. 4,245,510 relates to a portable accelerometer device mounted by suspension means in a housing and adapted for use to measure accurately the magnitude of a load applied to a vehicle, ship, floating bouy or some other transportation device. The device measures excursions from a datum due to an applied load on a vehicle and will overcome many of the problems associated with the use of stabilized platform assemblies for measuring vertical loads applied to towed bodies and/or the towing cable with its associated couplings. Applied vertical loads are measured by a mechanical pendulum assembly mounted by suspension in a housing and having an accelerometer as its load sensing device. An output signal is generated in response to displacements due to applied loads. This apparatus cannot be adapted for on-site drop tests and required skilled operators to conduct tests and analyze data obtained by the apparatus.
In Wilson et al U.S. Pat. No. 3,788,466 the device is one that is used in a material sorting system. An accelerometer is mounted on a movable, rigid, pendulum-like arm adapted to strike individual pieces of material moving along a conveyor system. The accelerometer measures the rate of deceleration of the pendulum-like arm as it strikes material producing a signal waveform. This signal is then fed to an electronic coding apparatus which compares this received waveform to typical waveforms stored in computer memory. When a match is made, the material is routed to its proper receptacle. The object of this invention is to provide a coding and switching system for use in automated, solid-refuse sorting.
Specker et al U.S. Pat. No. 4,161,874 relates to a head and neck impact measuring system consisting of a movable plate member with an anthropometric (dummy) head and neck secured to the plate. Force measuring cells are mounted in the horizontal and vertical planes of the supports and the dummy head and triaxial accelerometers at the CG of the dummy head. The device is for measuring head accelerations and impact forces to determine moments reacted through the base of the neck. The invention is primarily aimed at evaluation of injury potential to pilots and aircraft crew members in bird-aircraft midair collisions. These collisions often result in an impact of the aircraft canopy with the pilot's helmet.
In Yamawaki et al U.S. Pat. No. 4,11,039, a bench or laboratory apparatus for measuring the hardness of rubber is patented. This device provides an improved mechanism for measuring the hardness of rubber with a high degree of reliability and accuracy. The device provides a means of pressing a needle-like probe against the surface of a sample at a predetermined velocity and force and for maintaining the reaction of the sample acting on the needles at a constant value thereby increasing measurement accuracy. The measurement is detected by a transducer and processed by an electronic circuit eliminating errors induced by moving pointers and operator skill.
Fletcher's invention in U.S. Pat. No. 3,972,038 relates to an accelerometer telemetry system incorporated in a finger ring and is used for monitoring motor responses of a subject. The system includes an accelerometer, battery and transmitter and provides information to a remote receiver regarding hand movements of a subject wearing the ring. The system includes a miniaturized semiconductor strain gauge coupled to a seismic mass for detecting movements and for producing an electrical output signal. The output signal is used to modulate an RF transmitter. The entire sensing and transmitting package including the power sources is contained in a case or housing the size and shape of a finger ring.
Yakshin et al U.S. Pat. No. 4,030,339, relates to a device for automatic selection of the range of peak acceleration measurements. The object of the invention is to provide electronic circuitry which would make it possible to automatically select a required measurement range and thus increase the operating speed of impact impulse measurements. Automatic range selection is achieved through a series of amplifiers, comparators and D/A conversion circuitry.
Brands U.S. Pat. No. 3,888,108 relates to an apparatus for detecting transmission of an energy impulse through pavement as an indicator of its structural condition. Impact is provided by a hammer that falls vertically when manually released. A pair of spaced transducers operating as accelerometers in contact with the pavement produce electrical signals related to the magnitude of the energy impulse transmitted through the pavement to them. These signals are monitored, rectified, integrated, and used with readout circuitry to calculate a useful numerical value indicative of pavement structural conditions. In use, the device is hand-carried to a test site and the pavement excited with a shock wave or impulse provided by the falling hammer. The vibrational response is subjected to a complex wideband analysis to extract useful information concerning pavement strength. Skilled engineers are required to conduct the tests and to conduct the analyses necessary to determine structural conditions.
In Messner U.S. Pat. No. 3,365,929, the invention relates to a portable, impact shock testing device to provide for dynamically testing shock transducers in the field where conventional devices are either unavailable or their use was impractical. The tester is used principally for checking the output of the piezoelectric accelerometers immediately prior to field use. The output of the accelerometers undergoing test is connected to an oscilloscope for indicting the shock pulse. This is a device for testing transducers such as piezoelectric accelerometers and as such is not useful for on-site drop testing to obtain surface characteristics.
In Costello et al U.S. Pat. No. 3,298,222, the invention is an apparatus for measuring remote and relatively inaccessible surface characteristics to determine its load bearing properties. The device is comprised of a hydrodynamically designed vehicle which is dropped from a ship and allowed to gravitationally impact the surface beneath a body of water. An accelerometer or transducer on the device is connected by a cable to shipboard monitoring equipment. The signal thus produced is an indication of the load bearing characteristics of the bottom surface.
Falkner's invention of U.S. Pat. No. 3,149,606 relates to a simple shock device which gives an indication of when it has been subjected to a shock force of more than a given value. Such a device is particularly useful for showing whether cargo has been subjected to excessive shock during transit or handling. It consists of at least two weights which are spring loaded against supports so that a non-axial acceleration of more than a given value will displace a respective weight from its support and the consequent position of the weight will show that a pre-determined acceleration has been exceeded.
While the foregoing references describe various means of obtaining test measurements with impact devices, none are hand-portable or capable of obtaining multiple, on-site, drop test measurements of natural or synthetic surfaces nor are they capable of being dropped from various heights to simulate head-first falls by children.